Method and system for turbocharging an engine

ABSTRACT

A method for improving operation of a turbocharged engine is presented. In one embodiment, the method may reduce engine emissions and improve engine efficiency during an engine start.

FIELD

The present description relates to a method for improving operation of aturbocharged engine. The method may be particularly useful for reducingengine emissions and increasing engine efficiency after a cold start.

BACKGROUND AND SUMMARY

One way to increase engine efficiency is to reduce engine displacementand boost the engine. However, placing a turbine in an exhaust systemcan increase engine emissions and reduce engine efficiency during anengine start. In particular, engine emissions can be increased since theturbocharger may sink engine exhaust heat during an engine start ratherthan passing the exhaust heat to a catalyst to promote oxidation andreduction of exhaust gas constituents. Further, engine efficiency can bereduced when spark is retarded or air mass flow through the engine isincreased to warm the mass of the turbocharger. Thus, engine boostingcan make it more difficult to meet engine emissions and improve engineefficiency during engine starting.

The inventors herein have recognized the above-mentioned disadvantagesand have developed an engine method, comprising: opening a first exhaustvalve of a cylinder before a piston of the cylinder reaches BDCcompression stroke of the cylinder; directing exhaust gases across thefirst exhaust valve into a first conduit; recovering heat from theexhaust gases in the first conduit to a liquid; and returning theexhaust gases to a second conduit that is in communication with a secondexhaust valve of the cylinder.

Engine efficiency can be increased while engine emissions are reduced byseparating the exhaust ports of a cylinder and separately processingblow down (e.g., expanding exhaust gases in a cylinder before time whena piston of the cylinder reaches bottom dead center expansion stroke)and residual exhaust gases (e.g., gases that remain in the cylinderafter blow-down). In particular, exhaust energy can be transferred fromthe blow-down gases to operate a turbocharger or to reduce enginefriction by quickly warming the engine via an exhaust heat recoverydevice such as a gas-to-liquid heat exchanger. At the substantially sametime, residual gases are directed from a second exhaust port of thecylinder to heat a catalyst, thereby reducing engine emissions. In thisway, exhaust gases can be used more efficiently than simply directingall the exhaust gas of a cylinder to a turbocharger.

The present description may provide several advantages. For example, theapproach may improve fuel economy and reduce particulate emissions bydecreasing engine warm-up time. Further, the method can reduce engineemissions since at least a portion of cylinder exhaust gases aredirectly routed from the cylinder to the catalyst. Further still, theaverage exhaust gas pressure supplied to the turbocharger can beincreased to improve turbocharger output.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment, referred to herein as the DetailedDescription, when taken alone or with reference to the drawings, where:

FIG. 1A is a schematic diagram of one cylinder of an engine;

FIG. 1B is a schematic diagram of a four cylinder engine;

FIG. 2 shows simulated signals of interest when operating an engine;

FIG. 3 shows additional simulated signals of interest when operating anengine;

FIG. 4A is an example flowchart of a method for operating an engine; and

FIG. 4B is a continuation of the flowchart shown in FIG. 4A.

DETAILED DESCRIPTION

The present description is related to operating an engine. In onenon-limiting example, the engine may be configured as illustrated inFIGS. 1A and 1B. In one example, blow-down gases of a cylinder areseparated from residual cylinder gases and the engine is operatedaccording to the methods of FIGS. 4A-4B providing the signals of FIGS.2-3.

Referring to FIG. 1A, a single cylinder of an internal combustion engine10 is shown. Internal combustion engine 10 is comprised of a pluralityof cylinders as shown in FIG. 2. Engine 10 includes combustion chamber30, coolant sleeve 114, and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 80 viarespective intake valves 52 and exhaust valves 54. Each intake andexhaust valve may be operated by an intake cam 51 and an exhaust cam 53.Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 51 may be determined by intake camsensor 55. The position of exhaust cam 53 may be determined by exhaustcam sensor 57. In one example, exhaust cam 53 includes separate anddifferent cam lobes that provide different valve profiles for each oftwo exhaust valves for combustion chamber 30. For example, a first camprofile of a first exhaust valve of combustion chamber 30 has a firstlift amount and a first opening duration. A second cam profile of asecond exhaust valve of combustion chamber 30 has a second lift amountand a second opening duration, the first lift amount less than thesecond lift amount and the first opening duration less than the secondlift duration. In addition, in some examples, the phase of the first andsecond cam profiles may be individually adjusted relative to the phaseof the engine crankshaft. Thus, the first cam profile can be positionedto open the exhaust valve BDC of the expansion stroke of combustionchamber 30. In particular, the first cam profile can open and close afirst exhaust valve before BDC expansion stroke. Further, the first camprofile can be adjusted in response to engine speed to adjust exhaustvalve opening and closing to selectively exhaust blow-down gas ofcombustion chamber 30. On the other hand, the second cam profile canopen a second exhaust valve after BDC expansion stroke. Thus, the timingof the first exhaust valve and the second exhaust valve can isolatecylinder blow-down gases from residual gases.

In an example where engine warm-up is not the priority mode, themajority of the initial blow-down energy is directed to the turbine. Theremainder of expelled exhaust gas emerges at a low pressure and isdirectly routed to the exhaust after treatment with bypassing theturbine. The higher pressure exhaust gas is also optionally deployableas EGR or heatant for warming transmission fluid, engine oil, coolant,or engine air via a heat exchanger.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width signal. Fuel isdelivered to fuel injector 66 by a fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown). Distributorlessignition system 88 provides an ignition spark to combustion chamber 30via spark plug 92

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 46, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Blow-down gases may be releasefrom the cylinder before the cylinder reaches BDC if desired by openingat least one exhaust valve of an exhaust valve pair. Further, during theexhaust stroke, the other exhaust valve of an exhaust valve pair opensto release the residual combusted air-fuel mixture to exhaust manifold80 and the piston returns to TDC. Note that the above is shown merely asan example, and that intake and exhaust valve opening and/or closingtimings may vary, such as to provide positive or negative valve overlap,late intake valve closing, or various other examples.

Referring now to FIG. 1B, a schematic diagram of a four cylinder enginecomprised of cylinders configured with cylinders as shown in FIG. 1A isshown. Engine 10 includes cylinder number one 12 with intake I valvesand exhaust E valves. Likewise, cylinder number two 14, cylinder numberthree 16, and cylinder number four 18 include intake I and exhaust Evalves. Cylinders are supplied air via intake manifold 44. In addition,intake manifold 44 is shown communicating with optional electronicthrottle 62 which adjusts a position of throttle plate 64 to control airflow from intake boost chamber 46. Compressor 162 draws air from airintake 42 to supply intake boost chamber 46. Exhaust gases spin turbine164 which is coupled to compressor 162. A high pressure, dual stage,fuel system may be used to generate fuel pressures at injectors 66.

Distributorless ignition system 88 provides an ignition spark tocylinders 12, 14, 16, and 18 via sparks plug 92 in response tocontroller 20. Exhaust from cylinders 12, 14, 16, and 18 is directed toexhaust manifolds 80 and 84 via exhaust runners 82 and 86. Exhaustrunners 82 extend from cylinders 12, 14, 16, and 18 to exhaust manifold80. Exhaust runners 86 extend from cylinders 12, 14, 16, and 18 toexhaust manifold 84. Exhaust runners 82 are isolated from exhaustrunners 86 when at least one exhaust valve of each cylinder is in aclosed position. Accordingly, exhaust from cylinders 12, 14, 16, 18exits to exhaust runners 82 and 86 and only recombines downstream ofvalves 140 or 144 in the direction of exhaust flow. Alternatively, whenexhaust gas recirculation is present by opening exhaust gasrecirculation (EGR) valve 142, exhaust gases may flow to exhaust runners82 and enter intake manifold 44. After entering intake manifold 44,exhaust gases may enter exhaust runners 86 after combustion events incylinders 12, 14, 16, and 18. Thus, exhaust gases may not flow directlybetween exhaust runners 82 and 86.

The Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 84 upstream of catalysts 70 and 72. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126. Turbocharger turbine 164 receives exhaust gases from exhaustmanifold 80 to power air compressor 162. Exhaust gas heat recoverydevice 146 also receives exhaust gases from exhaust manifold 80. In oneexample, exhaust gas heat recovery device is a gas-to-liquid heatexchanger. In another example, exhaust gas heat recovery device is a gasto gas heat exchanger. In still another example, exhaust gas heatrecovery device 146 may be a Peltier device.

EGR valve 142, heat recovery valve (HRV) 140, and positive turbineshut-off valve 144 control the flow of exhaust gases from exhaustmanifold 80. Exhaust from exhaust manifold 80 may flow to intakemanifold 44 via conduit 158 when EGR valve 142 is in an open position.Exhaust from exhaust manifold 80 may flow to turbine 164 via conduit 150when turbine shut-off valve 144 is in an open position. Exhaust fromexhaust manifold 80 may flow to conduit 152 when HRV is in an openposition.

Converters 70 and 72 can include multiple catalyst bricks, in oneexample. In another example, multiple emission control devices, eachwith multiple bricks, can be used. Converters 70 and 72 can be athree-way type catalyst in one example.

Controller 20 is shown in FIG. 1B as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 20 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) from atemperature sensor (not shown); a position sensor 134 coupled to anaccelerator pedal 130 for sensing force/deflection applied by foot 132;a measurement of engine manifold absolute pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; a measurement of boostpressure from pressure sensor 123; a measurement of air mass enteringthe engine from sensor 120; and a measurement of throttle position froma sensor (not shown). Barometric pressure may also be sensed (sensor notshown) for processing by controller 20. In a preferred aspect of thepresent description, an engine position sensor (not shown) produces apredetermined number of equally spaced pulses every revolution of thecrankshaft from which engine speed (RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof. Further, in some embodiments, other engine configurations maybe employed, for example a diesel engine.

Thus, the system of FIGS. 1A and 1B provides for an engine system,comprising: a first exhaust conduit extending from a first exhaust portof a cylinder; a second exhaust conduit extending from a second exhaustport of the cylinder, the second exhaust port isolated from the firstexhaust port; a gas-to-liquid heat exchanger located in a first branchof the first exhaust conduit, an outlet of the gas-to-liquid heatexchanger directed to an intake manifold and the second conduit; aturbocharger located in a second branch of the first exhaust conduit;and a first catalyst and a second catalyst located along the secondconduit. The engine system further comprises a first valve locateddownstream of the turbocharger in a direction of exhaust flow, and asecond valve located between the gas-to-liquid heat exchanger and theintake manifold, and a third valve located between the gas-to-liquidheat exchanger and second conduit. The engine system further comprises acontroller including instructions for operating the first, second, andthird valves such that a first portion of exhaust gases from thecylinder are directed to the intake manifold, a second portion of theexhaust gases from the cylinder are directed to the turbocharger. Theengine system includes where the outlet of the gas-to-liquid heatexchanger is directed to a location in the second conduit upstream ofthe first catalyst in a direction of exhaust flow from the secondexhaust port of the cylinder, and where an outlet of the turbocharger isdirected to a location in the second conduit downstream of the firstcatalyst and upstream of the second catalyst in a direction of exhaustflow from the second exhaust port to the first catalyst. The enginesystem further comprises an EGR valve positioned intermediate the intakemanifold and the gas-to-liquid heat exchanger. The engine system furthercomprises a controller including instructions for closing the firstvalve during a start of an engine where a temperature of the engine isless than a threshold amount.

Referring now to FIGS. 2 and 3, simulated signals of interest whenoperating an engine are shown. For each plot shown in FIGS. 2 and 3,time begins at the right side of the plot and increases to the left.

The first plot from the top of FIG. 2 represents desired engine torque.Desired engine torque may be determined from an operator's depression ofa pedal or from a signal of a system (e.g., a hybrid vehiclecontroller). The second plot from the top of FIG. 2 represents enginespeed. The third plot from the top of FIG. 2 represents enginetemperature. The horizontal dotted line 202 in the engine temperatureplot represents a threshold engine temperature. The fourth plot from thetop of FIG. 2 represents desired engine boost. The fifth plot from thetop of FIG. 2 represents the position of a turbine shut-off valve (TSV).The TSV is open when the illustrated signal is at a higher level. TheTSV is closed when the illustrated signal is at a lower level. Thefirst, second, and third plots from the top of FIG. 3 are the same asthe first three plots from the top of FIG. 2. The plots are repeated toimprove the viewer's identification of selected operating conditions.The fourth plot from the top of FIG. 3 represents the position of theexhaust heat recovery valve (HRV). The HRV is open when the illustratedsignal is at a higher level. The HRV is closed when the illustratedsignal is at a lower level. The fifth plot from the top of FIG. 3represents the position an EGR valve. The verticals markers near T₁-T₅are provided to show timing of events of interest.

At time T₀, the engine is started from cold operating conditions. Noticethat engine temperature is near the bottom of the engine temperatureplot so as to indicate a cooler engine temperature. As time increases tothe right, engine temperature increases as the engine warms up. Thedesired engine torque is also at a low level indicating that theoperator or other system is not requesting much engine torque (e.g.,when the engine is idling). Accordingly, the desired engine boost isalso low at T₀. The turbine shut-off valve is in a low state at T₀indicating that the valve is in a closed position. By closing theturbine shut-off valve, more exhaust heat may be directed to the exhaustgas heat recovery device. Similarly, the EGR valve position signal is ata low level indicating that the EGR valve is closed. At colder enginetemperatures and after an engine start, an engine may have lesstolerance for EGR. Thus, the EGR valve is closed in this example. On theother hand, the HRV is set to an open position to allow exhaust gases totransfer energy to the exhaust heat recovery device during the enginestart so that energy from the exhaust can be transferred to enginecoolant, engine oil, transmission oil or other areas that may exhibithigher friction at lower temperatures. Further, returning exhaust heatto the engine when the engine is cold can reduce particulate emissions.Therefore, in one example, the HRV valve can be controlled to returnexhaust heat to the engine until a threshold temperature at whichparticulate emissions for a specified engine load are less than athreshold level.

At time T₁, the desired engine torque signal begins to transition to ahigher level indicating an increase in desired engine torque. Atsubstantially the same time, the engine speed begins to increase. Theengine speed and desired engine torque continue to increase until alevel of desired torque is reached. When the desired boost reaches alevel where it is desirable to start powering up the turbocharger, theturbine shut-off valve is opened to activate the turbocharger.Consequently, the TSV opens at T₂ as indicated by the TSV signaltransitioning from a low level signal to a high level signal. Atsubstantially the same time, the HRV begins to close so that additionalamounts of exhaust gas can be directed to the turbocharger turbine.Between time T₂ and time T₃, the HRV continues to close as desiredengine torque, desired boost, and engine speed increase. In addition,engine temperature continues to increase and the EGR valve is opened asindicated by the EGR valve position signal increasing.

At time T₃, the desired engine torque falls as do desired boost andengine speed. Desired engine torque may decrease in response an operatortipping out (e.g., at least partially releasing) of a throttle or apedal. In response to less desired torque, the EGR valve position closesand the HRV opens. When the desired level of torque is low, the engineneeds less air to provide a desired level of torque. As a result, theengine may be able to tolerate less EGR. Consequently, additionalexhaust may be directed to the exhaust heat recovery device since theengine requires less exhaust gas. Between times T₃ and T₄, the engine isoperated at a low load (e.g., during a deceleration).

At time T₄, the engine load begins to increase as do desired boostpressure, engine speed, and engine speed. Consequently, more exhaustenergy is required to meet the boost demand so the HRV begins to close,thereby increasing the exhaust energy supplied to the turbine.

At time T₅, the engine reaches a threshold temperature as indicated byhorizontal dotted line 202. In one example, the engine is at operatingtemperature when it reaches the temperature indicated by horizontal line202. Consequently, exhaust heat is no longer supplied to the engine ortransmission as indicated by the HRV substantially closing at T₅. TheEGR valve position indicates that the EGR valve is opened between T₄ andT₅. Thus, exhaust may be directed to the intake manifold and to theturbine after time T₄. The method described in FIGS. 4A and 4B iscapable of operating according to the plots of FIGS. 2 and 3.

Referring now to FIG. 4A, an example flowchart of a method for operatingan engine is shown. The numerical identifiers used in the description ofFIG. 4 are based on the system of FIG. 1A.

This method prioritizes engine torque when demanded by the vehicleoperator. When the operator desired torque level is satisfied by enginetorque output, warm-up is prioritized by directing the path of exhaustgases. Warm-up control of exhaust gases ceases when a threshold enginetemperature is reached. EGR control continues after the engine is warmedup.

At 402, engine operating conditions are determined. Engine operatingconditions may include but are not limited to a temperature of theengine, atmospheric temperature and pressure, engine speed, engine load,time since engine start, number of combustion events since the enginewas last stopped, intake manifold pressure, desired engine torque,engine load, boost pressure, and throttle position. Routine 400 proceedsto 404 after engine operating conditions are determined.

At 404, routine 400 judges whether or not engine temperature is lessthan a threshold temperature. For example, if engine temperature is lessthan a threshold temperature of 20 degrees C., routine 400 proceeds to406. Otherwise, routine 400 proceeds to 418.

At 406, routine 400 judges if EGR is desired. In one example, EGR isdesired during predetermined engine operating conditions. For example,when engine coolant temperature is greater than a threshold temperature,when engine load is greater than a first threshold engine load and lessthan a second threshold engine load, and when engine speed is greaterthan a first threshold engine speed and less than a second thresholdengine speed. If routine 400 judges that EGR is desired, routine 400proceeds to 422 of FIG. 4B. Otherwise, routine 400 proceeds to 408.

At 408, routine 400 judges if boost is desired. In one example, anamount of boost provided by a compressor such as a turbocharger may bedetermined in response to an operator engine torque demand from a pedalsensor or other device. In another example, an amount of boost may bedetermined in response to a hybrid controller. If boost is desired,routine 400 proceeds to 410. Otherwise, routine 400 proceeds to 414.

At 410, routine 400 judges whether or not desired boost is greater thana threshold amount. In one example, the threshold amount of boost isrelated to a higher level of desired torque so that substantially fullengine power is available to the operator. In another example, thethreshold amount of boost may be related to an engine temperature oranother engine operating condition. If the desired boost is greater thana threshold amount, routine 400 proceeds to 412. Otherwise, routine 400proceeds to 416.

At 412, routine closes a heat recovery valve, opens a turbine shut-offvalve, closes an EGR valve, and adjusts the turbocharger to provide thedesired level of boost. By closing the heat recovery valve at 412 andEGR valve 142, substantially all exhaust energy in exhaust manifold 80can be directed to turbine 164. As such, engine power output may beincreased by allowing compressor 162 to provide higher levels of boostto the engine. In one example, the turbine waste gate or vane positioncan be adjusted in response to a difference between a desired boostpressure and an observed or measured boost pressure. The desired boostpressure can be determined from empirically determined boost values thatare indexed by engine speed and desired engine torque.

In one example at 412, the cam phase of exhaust valves that control flowinto exhaust runners 82 can be adjusted to vary timing of when blow-downgases are released to exhaust runners 82 from cylinders 12, 14, 16, and18. In particular, at lower engine speeds exhaust timing of valves thatcontrol exhaust flow to exhaust runners 82 can be such that the exhaustvalve opens relatively late and closes substantially at BDC expansionstroke of the cylinder. At higher engine speeds exhaust timing of valvesthat control exhaust flow to exhaust runners 82 can be such that theexhaust valve opens relatively early and closes before BDC expansionstoke of the cylinder. Thus, the timing of the exhaust valves thatcontrol exhaust flow to exhaust runners 82 is retarded at lower enginespeeds.

The timing of exhaust valves that control flow from cylinders 12, 14,16, and 18 to exhaust runners 86 can also be adjusted at 412. Inparticular, valves controlling exhaust gas flow to exhaust runners 86are also retarded at lower engine speeds. In particular, valvescontrolling exhaust gas flow to exhaust runners 86 are opened atsubstantially BDC exhaust stroke at lower engine speeds. At higherengine speeds, valves controlling exhaust gas flow to exhaust runners 86are opened before BDC exhaust stroke. Thus, the exhaust valves thatcontrol exhaust gas flow to exhaust runners 82 control the flow ofblow-down gases from cylinders 12, 14, 16, and 18 to exhaust manifold80. And, the exhaust valves that control exhaust gas flow to exhaustrunners 84 control the flow of residual gases from cylinders 12, 14, 16,and 18 to engine exhaust manifold 84. By separating the blow-down gasfrom the residual gas, exhaust gases with higher energy can be directedto the turbine and the exhaust heat recovery device.

At 416, routine 400 opens the heat recovery valve, closes the EGR valve,opens the turbine shut-off valve, and adjusts the turbocharger. Thus, at416 it is desirable to provide boost and recover heat energy from theexhaust. Heat energy from the exhaust may be used to more quickly warmthe engine by transferring the heat energy to the engine coolant.Further, the exhaust heat energy may be used to heat the transmission.In these ways, the exhaust gas may be used to reduce engine frictionduring a cold start.

In one example, the HRV (e.g., 140 of FIG. 1B) can be adjusted tooperate similar to a turbocharger waste gate so that exhaust gas energythat is not needed to provide a desired level of boost is provided tothe exhaust heat recovery device. For example, if the turbine isproviding or capable of providing a desired level of boost with lessthan the amount of exhaust gas provided by the engine via exhaustmanifold 80, then the exhaust gas heat recovery valve 140 can be atleast partially opened to allow flow through the exhaust heat recoverydevice 146. When the exhaust heat recovery valve acts as a turbinebypass for a portion of exhaust gases traveling through exhaust manifold80, the waste gate or vanes of turbine 164 can be set such that theturbine is operating at substantially its highest efficiency given theexhaust flow to the turbine. For example, the turbine waste gate can beclosed or the vanes can be set at a highly efficient position. Further,if the engine is operating at cold start conditions, the turbineshut-off valve may be closed until the engine reaches a desired enginespeed or temperature so that substantially all the exhaust heat isrecovered by the exhaust heat recovery device 146.

In another example, the HRV is adjusted so that a proportion of theexhaust energy is directed to the exhaust heat recovery device. Forexample, the HRV position can be adjusted in response to engine load ordesire engine torque so that a portion of exhaust energy is directed toheat recovery device 146 while the remainder of the exhaust gas energyis directed to the turbine 164. Of course, the percentage of exhaustgases directed to the heat recovery device can be varied depending onengine operating conditions. For example, if the engine is cold thepercentage of exhaust gases directed to the exhaust gas heat recoverydevice can be higher than the percentage of exhaust gases directed tothe turbine. Under substantially the same engine operating conditions,but at a higher engine temperature, the percentage of exhaust gasesdirected to the turbine can be greater than the percentage of exhaustgases directed to the exhaust gas heat recovery device.

At 414, routine 400 closes the EGR valve, opens the HRV, and closes theEGR valve. Since EGR and boost are not required at 414, substantiallyall exhaust energy in exhaust manifold 80 can be directed to the exhaustgas heat recovery device 146. This mode of operation may be particularlyuseful during engine starting because a higher amount of exhaust gasenergy can be recovered by the exhaust gas heat recovery device.

At 422, routine 400 judges whether or not boost is desired. In oneexample, an amount of boost is determined as described at 408. Inparticular, boost may be determined in response to an operator enginetorque demand from a pedal sensor or other device or in response to ahybrid controller. If boost is desired, routine 400 proceeds to 428.Otherwise, routine 400 proceeds to 424.

At 428, routine 400 opens the EGR valve, opens the HRV valve, and opensthe turbine shut-off valve. Thus, routine 400 can provide EGR, turbinepower, and recovered exhaust heat at least under some conditions. In oneexample, priority can be assigned to EGR, boost, and exhaust heatrecovery during different operating conditions. For example, an amountof exhaust energy used to provide boost can be given higher priority ascompared to exhaust for EGR and the amount of exhaust for EGR can begiven priority over the amount of exhaust provided to the exhaust gasheat recovery device. Thus, if the amount of exhaust heat energyprovided by the engine to exhaust manifold is insufficient to operatethe turbine, the EGR valve, and the exhaust heat recovery device undersome engine operating conditions, the available exhaust energy can bedirected to areas with higher priority by at least partially closingeither the EGR valve, the HRV, or the turbine shut-off valve. In oneexample, the amount of available exhaust energy can be determined basedon engine load and exhaust valve timing.

In one example, a desired pressure in exhaust manifold 80 is establishedin response to engine operating conditions (e.g., engine speed anddesired engine torque). Further, the EGR valve position is adjusted inresponse to a desired EGR flow rate and a pressure differential betweenexhaust manifold 80 and intake manifold. The HRV valve position isvaried to maintain the desired exhaust pressure in exhaust manifold 80.During conditions where the desired pressure of manifold 80 cannot bemaintained by adjusting the HRV, the HRV may be closed.

At 424, routine 400 closes the turbine shut-off valve. By closing theturbine shut-off valve, additional exhaust gases can be directed to EGRand heat recovery. Routine 400 proceeds to 426 after the turbineshut-off is shut off.

At 426, routine 400 adjusts the EGR valve and the HRV proportionally toprovide EGR and recovered exhaust heat. In particular, the EGR valve isadjusted to provide the desired EGR flow rate by adjusting the positionof the EGR valve in response to a desired EGR flow rate and the pressuredifferential between the exhaust manifold 80 and the intake manifold 44.The HRV is adjusted to provide a desired level of pressure in exhaustmanifold 80. The desired level of pressure in the exhaust manifold isdetermined in response to engine speed and desired torque. Thus, the HRVis adjusted in response to engine speed and desired torque to provide adesired level of pressure in exhaust manifold 80.

At 418, routine 400 opens the turbine shut-off valve, closes the HRV.The HRV valve is closed to increase the level of exhaust energy suppliedto the EGR valve and the turbine. In this way, the output of the turbinemay be increased. Routine 400 proceeds to 420 after the turbine shut-offvalve is opened and after the HRV is closed.

At 420, routine 400 adjusts the EGR valve position and the turbocharger.The EGR valve position is adjusted based on a desired EGR rate and thepressure differential between the intake manifold 44 and the exhaustmanifold 80. The turbine waste gate is adjusted according to desiredboost pressure and compressor speed. In one example, the waste gate isopened when compressor speed exceeds a threshold. Further, the wastegate is opened in response to boost pressure exceeding a desired boostpressure.

Thus, the methods of FIGS. 4A and 4B provides for an engine method,comprising: opening a first exhaust valve of a cylinder before a pistonof the cylinder reaches BDC compression stroke of the cylinder;directing exhaust gases across the first exhaust valve into a firstconduit; recovering heat from the exhaust gases in the first conduit toa liquid; and returning the exhaust gases to a second conduit that is incommunication with a second exhaust valve of the cylinder. The enginemethod also includes where the first exhaust valve is closed at orbefore BDC compression stroke of the cylinder. The engine methodincludes where the second exhaust valve of the cylinder opens after BDCexhaust stroke of the cylinder. The engine method includes where aportion of the exhaust gases are directed to an intake manifold of aturbocharged engine. The engine method includes where the heat isrecovered via a gas-to-liquid heat exchanger. The engine method includeswhere the portion of the exhaust gases are returned to the exhaustpassage in communication with the second exhaust valve at a locationupstream of a first catalyst in a direction of exhaust flow. The enginemethod includes where a portion of the exhaust gases are directed to aturbine and bypass the gas-to-liquid heat exchanger.

The method of FIGS. 4A and 4B also provides for an engine method,comprising: during a first mode, opening a first exhaust valve of acylinder before a piston of the cylinder reaches BDC compression strokeof the cylinder; flowing exhaust gases from a first combustion in thecylinder across the first exhaust valve; recovering heat from theexhaust gases from the first combustion to a liquid; returning theexhaust gases from the first combustion to an exhaust passage incommunication with a second exhaust valve of the cylinder, the exhaustgases from the first combustion bypassing a turbine; during a secondmode, opening a first exhaust valve of a cylinder before a piston of thecylinder reaches BDC compression stroke of the cylinder; flowing exhaustgases from a second combustion in the cylinder across the first exhaustvalve; and returning the exhaust gases from the second combustion to theexhaust passage in communication with the second exhaust valve of thecylinder bypassing a gas-to-liquid heat exchanger. The engine methodincludes where during the second mode, the exhaust gases from the secondcombustion are introduced to the exhaust passage in communication withthe second exhaust valve at a location downstream of a first catalyst ina direction of exhaust flow from the second exhaust valve. The engineincludes where during the first mode, a turbine shut-off valve is in aclosed position, and where during the second mode the turbine shut-offvalve is in an open position. The engine method includes where duringthe first mode, an EGR valve downstream of gas-to-liquid heat exchangerin the direction of exhaust flow is closed. The engine method includeswhere during the first mode, the exhaust gases from the first combustionare returned to the exhaust passage in communication with the secondexhaust valve of the cylinder at a location upstream of a first catalystin a direction of exhaust flow from the second exhaust valve. The enginemethod includes where during the second mode, the exhaust gases from thefirst combustion are returned to the exhaust passage in communicationwith the second exhaust valve of the cylinder at a location downstreamof a first catalyst in a direction of exhaust flow from the secondexhaust valve. The engine method further comprises directing a portionof the exhaust gases from the first combustion to an intake manifold.

As will be appreciated by one of ordinary skill in the art, routinesdescribed in FIGS. 4A-4B may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1-20. (canceled)
 21. An engine method, comprising: opening a firstexhaust valve of a cylinder before a piston reaches BDC expansion strokeof the cylinder; directing exhaust gases across the first exhaust valveinto a first conduit; and recovering heat from the exhaust gases in thefirst conduit to a liquid, and then returning the cooled exhaust gasesto a second conduit that is in communication with a second,later-opening, exhaust valve of the cylinder.
 22. The engine method ofclaim 21, where the exhaust gases directed across the first exhaustvalve are separated from exhaust gases directed across the secondexhaust valve at least until the exhaust gases directed across the firstexhaust valve pass through a valve.
 23. The engine method of claim 21,where the second exhaust valve of the cylinder opens after BDC exhauststroke of the cylinder.
 24. The engine method of claim 21, where aportion of the exhaust gases are directed to an intake manifold of aturbocharged engine.
 25. The engine method of claim 21, where the heatis recovered via a gas-to-liquid heat exchanger.
 26. The engine methodof claim 21, where the portion of the exhaust gases are returned to theexhaust passage in communication with the second exhaust valve at alocation upstream of a first catalyst in a direction of exhaust flow.27. The engine method of claim 25, where a portion of the exhaust gasesare directed to a turbine and bypass the gas-to-liquid heat exchanger.28. An engine system, comprising: a first cam profile in communicationwith a first exhaust valve in a first exhaust port of a cylinder; asecond cam profile in communication with a second valve in a secondexhaust port of the cylinder; a first exhaust conduit extending from thefirst exhaust port of the cylinder; a second exhaust conduit extendingfrom the second exhaust port of the cylinder, the second exhaust portisolated from the first exhaust port; a gas-to-liquid heat exchangerlocated in a first branch of the first exhaust conduit, an outlet of thegas-to-liquid heat exchanger directed to an intake manifold and thesecond conduit; a turbocharger located in a second branch of the firstexhaust conduit; and a first catalyst and a second catalyst locatedalong the second conduit.
 29. The engine system of claim 28, furthercomprising a first valve located downstream of the turbocharger in adirection of exhaust flow, and a second valve located between thegas-to-liquid heat exchanger and the intake manifold, and a third valvelocated between the gas-to-liquid heat exchanger and the second conduit.30. The engine system of claim 29, further comprising a controllerincluding instructions for operating the first, second, and third valvessuch that a first portion of exhaust gases from the cylinder aredirected to the intake manifold, and a second portion of the exhaustgases from the cylinder are directed to the turbocharger.
 31. The enginesystem of claim 28, where the outlet of the gas-to-liquid heat exchangeris directed to a location in the second conduit upstream of the firstcatalyst in a direction of exhaust flow from the second exhaust port ofthe cylinder, and where an outlet of the turbocharger is directed to alocation in the second conduit downstream of the first catalyst andupstream of the second catalyst in a direction of exhaust flow from thesecond exhaust port to the first catalyst.
 32. The engine system ofclaim 31, further comprising an EGR valve positioned intermediate theintake manifold and the gas-to-liquid heat exchanger.
 33. The enginesystem of claim 29, further comprising a controller includinginstructions for closing the first valve during a start of an enginewhere a temperature of the engine is less than a threshold amount. 34.An engine method, comprising: opening and closing a first exhaust valveof a cylinder before a piston reaches BDC expansion stroke of thecylinder; directing gases across the first exhaust valve into a firstconduit; and recovering heat from the gases in the first conduit to aliquid, and then returning the cooled gases to a second conduit that isin communication with a second, later-opening, exhaust valve of thecylinder.
 35. The engine method of claim 34, where the opening timing ofthe first exhaust valve is varied with engine speed.
 36. The enginemethod of claim 35, where timing of the first exhaust valve is retardedat lower engine speeds and advanced at higher engine speeds.
 37. Theengine method of claim 34, where the opening timing of the secondexhaust valve is retarded at lower engine speeds and advanced at higherengine speeds.